How about a meadow? If you look up GoY member Jacque you'll get an idea of what I mean. It needn't look neglected - if you look at Jacque's you'll see she's mowed paths around the edges and through the long grass and planted wildflowers. It looks beautiful in her photos. And you'd only have to mow it once or twice a year!

if you dont want grass why not have a gravel garden and put alpines and rockery plants about, also a few planters, birdbath and statue,

I had the same large area that because of work it was hard to keep up to so I put decking down and I have now an area for barbecues etc and also about 20 plant tubs it look brilliant